This invention relates to a semiconductor laser having a resonator constructed on and vertical to a substrate surface.
In conventional semiconductor lasers a resonator is constructed in a plane parallel to a substrate surface. With the development of crystal growing techniques recently it has become possible to construct a resonator structure on a substrate surface in the direction vertical to the substrate surface. Herein such a resonator will be called a vertical resonator.
A known vertical resonator has a first reflector mirror on the surface of a substrate, an active layer on the first mirror and a second reflector mirror on the active region. For example, on a GaAs substrate the first mirror is a reflective multilayer laminate formed of alternately arranged GaAs layers and AlAs layers. The active region has quantum wells of InGaAs sandwiched between two AlGaAs layers. The second mirror includes a reflective multilayer laminate formed of alternately arranged GaAs layers and AlAs layers, a metal electrode layer at the top and a spacing layer of GaAs which interposes between the reflective multilayer laminate and the metal electrode layer. In each mirror the reflective multilayer laminate consists of quarter-wave layers, and the total number of layers is about 10 to 20. The first mirror is doped into n-type and the second mirror into p-type. After forming all the layers for the resonator the layers of the second mirror and the active region are mesa etched to thereby obtain a vertical resonator structure in which transverse mode of oscillation is confined With this vertical resonator the oscillation wavelength is about 950 nm, and laser light is emitted toward the substrate.
In a semiconductor laser with the above described vertical resonator the material of every layer is isotropic, and there is no anisotropy in any transversal plane of the vertical resonator. Therefore, the direction of polarization of the emitted laser light is indefinite, and for this reason the application of the semicondutor lasers of this type to optical devices or systems is restricted.